Carburetor idle system control

ABSTRACT

A downdraft-type carburetor has an idle system including an emulsion passage that is relatively large in diameter in comparison to a reduced diameter outlet from the emulsion passage that is connected to the main induction passage below the throttle valve, the emulsion passage containing a fuel jet that directs the fuel stream axially through the center of the emulsion passage to essentially eliminate wetting of the walls with fuel to thereby minimize random fluctuations of the fuel flow and provide a more finite control of idle fuel flow.

United States Patent Laszlo l-lideg Dearborn Heights, Mich. 789,262

Jan. 6, 1969 Jan 12, 197 1 Ford Motor Company Dearborn, Mich.

a corporation of Delaware Inventor Appl. No. Filed Patented Assignee CARBURETOR IDLE SYSTEM CONTROL 3 Claims, 5 Drawing Figs.

261/41 F02m 3/08 Field ofSearch 261/41.4

References Cited UNITED STATES PATENTS 7/l932 Geiger 1,935,350 11/1933 Chandler 26l/4l(.4)X

2,066,003 12/1936 Heftler 261/4l(.4)X 2,127,444 8/1938 Emerson 26l/4l(.4)X 2,568,987 9/1951 Brunner 261/41(.4) 2,701,709 2/1955 Brunner 261/41(.4) 2,852,240 9/1958 Goodyear 261/41(.4) 3,408,054 10/1968 Walker 261/4l(.4) 3,454,264 7/1969 Sarto Primary Examiner-Tim R. Miles Attorneys-John R. Faulkner and Robert E. McCollum ABSTRACT: A downdraft-type carburetor has an idle system 1 including an emulsion passage that is relatively large in diameter in comparison to a reduced diameter outlet from the emulsion passage that is connected to the main induction passage below the throttle valve, the emulsion passage containing a fuel jet that directs the fuel stream axially through the center of the emulsion passage to essentially eliminate wetting of the walls with fuel to thereby minimize random fluctuations of the fuel flow and provide a more finite control of idle fuel flow.

1 CARBURETOR IDLE SYSTEM CONTROL This invention relates, in general, to a carburetor for an internal combustion engine. More particularly, it relates to the idle system for such a carburetor.

In conventional fixed venturi-type carburetors, the rate of fuel discharge from the idle system fluctuates substantially with a relatively low frequency, for a reason to be explained. This results in a substantial variation of fuel-air ratio between engine cycles. To eliminate misfiring and engine roughness, therefore, the carburetor idle systems generally are calibrated so that the correct fuel-air ratio is-maintained during the leanest engine cycles. As a result, the rest of the engine cycles generally receive mixtures that are richer than desirable.

A major source of the random fuel discharge fluctuations from the idle system is the emulsion passage. The latter is the passage between the idle fuel jet and the idle system outlet hole which is connectedto the main induction passage down stream of the throttle plate. Air from the idle air bleed and fuel from the idle fuel jet flow through the emulsion passage and enter the carburetorbore through this outlet hole. The flow velocities are relatively low in the unrestricted emulsion passage and become high in the restricted outlet hole.

Most of the fuel flows along the walls of the low velocity portion of the emulsion passage. Because the air velocity is somewhat higher than the fuel velocity, the surface of the fuel film becomes rippled and unstable. Occasionally, plugs of liquid fuel are formed that cause a momentary change of air velocity. Furthermore, masses of liquid fuel accumulate in the side cavities of the emulsion passage, such as at the idle fuel jet cavity, the idle transfer slot cavity, and the cavity around the idle system outlet tapered adjustingscrew. The quantity of fuel in the side cavities varies because of the unstable balance of surface tension forces and drag forces caused by the airflow. The end result, therefore, is a random fluctuation of fuel flow rate through the emulsion passage. v v

In conventional idle systems, the time average rate of fuel discharge is substantially influenced by fuel temperature and fuel vapor pressure variation. An increase in the rate of fuel evaporation within the idle emulsion passage raises the vapor FIG. la is a cross-sectional viewof the carburetor portion illustrated in FIG. 1 with, however, the plane of viewing rotated slightly from that position shown in FIG. 1;

FIG. 2 and 2a are cross-sectional views corresponding to FIGS. 1 and la and illustrating a modified embodiment of the invention; and,

FIG. 3 is a cross-sectional view of a downdraft type carburetor illustrating a further modification of the invention.

FIG. 1 illustrates a portion of a conventional downdraft type carburetor that is commonly used with internal combustion engines of the axially reciprocable' piston type. More specifically, carburetor portion 10' includes the usual main air fuel induction passage 12. At its upper end 14, it is adapted to be connected through an air cleaner, not shown, to a source of air at essentially atmospheric pressure. At its lower end 16, it is adapted to be connected to the intake manifold of the engine so: as to be subject to the changing vacuum therein upon 1 changes in engine operation, in a known manner.

pressure and, therefore, tends to decrease the'idle metering signal; i.e., the pressure drop from the inlet to the outlet of the idle system. To. assure sufficient fuel flow in order to avoid misfiring and engine roughness at high fuel temperatures and high vapor pressures because of leanness, therefore, the idle fuel systems generally are adjusted to provide a richer mixture than desirable under average conditions.

. Automobile engines could be operated with leaner mixtures 'at light and medium loads if the random'fuel discharge fluctuation andthe fuel temperature and vapor pressure sensitivity of the idle fuel system was decreased. Leaner carburetor adjustment would improve the fuel economy and the exhaust gas composition. 1

It is a primary object of the invention, therefore, to achieve the improvements by providing acarburetor idle system constructed to substantially eliminate flow of liquid fuel on the walls and the accumulation of liquid fuel in side cavities of the low flow velocity section of the idle emulsion passage of an internal combustion engine type carburetor.

It is a further object of the invention to provide an internal combustion engine type carburetor with an improved idle system in which the idle fuel is injected essentially axially through the center of a straight and relatively large diameter emulsion passage and directly toward the outlet of the passage.

It is a still further object of the invention to provide an improved carburetor idle system having a low rate of fuel evaporation in the emulsion passage obtained by minimizing the wetting of the walls with fiiel. 4 7

Other objects, features and advantages of the invention will become more apparent upon reference to the succeeding detailed descriptionthereo f, and to the drawings illustrating the preferred embodiments thereof, wherein:

FIG. 1 is a cross-sectional view of aportion of a downdraft type carburetor embodying the invention;

Induction passage 12 also includes the usual fixed venturi section 18 and a throttle valve 20. ;The latter is rotatably mounted upon a shaft 22 joumaled in the sidewalls of the carburetor housing. Throttle valve 20 is movable between the engine idle speed position shown, essentially closing induction passage 12, and a wide open throttle position 24 indicated by dotted lines. 1

Further details of the main air fuel metering portion of the carburetor are not given since they are known and are believed to be unnecessary for an understanding of the invention. Suffice it to say, however, that the carburetor would include the usual main fuel discharge nozzle generally located in or adjacent venturi 18. The latter would be subject to the change in air flow through the venturi to meter the main supply of fuel to the engine, in a known manner.

Turningnow to the invention, and considering FIGS. 1 and in together, the idle system ofv the carburetor includes a relatively large diameter emulsion passage '26 that, in this instance, is essentially parallel to main induction passage 12. The upper end 28 of the passage is intersected by an air inlet passage 30 that is connected to the airhorn section 14 of the main induction passage so as to communicate with air at essentially atmospheric pressure. The air inlet passage contains the usual fixed area orifice 32 that provides a pressure drop thereacross and controls the vacuum signal in emulsion passage 26 in a manner to be described.

The lower portion of emulsion passage 26 is tapered to connect to a relatively small diameter outlet passage 34. The latter is intersected by a further passage 36 connected to induction passage 12. Passage 36 is, controlled in this case by a needle valve 38 slidably mounted in a side bore 40 through a seal 42. Passage 36 communicates with the main induction passage 12 ata' point below the closed position of throttle valve 20 so as always to be subject to the vacuum in the intake manifold of the engine. 1

As thus far described, therefore, the vacuum acting in passages 36 and 34 and emulsion passage 26, causes a pressure drop across the air'orifice 32 and'a' vacuum signal in emulsion tube 26 that varies as a function in the changes in the vacuum of intake manifold, in a known manner.

The upper end of emulsion passage 26 has mounted therein a fuel jet 44, which in this case, is in the form of a nozzle having an elongated orificed outlet 46. The upper end 48 of the fuel jet is open to a passage 50 containing fuel-52 supplied thereto from the carburetor fuel bowl, not shown. The fuel jet 44 constructed and positioned to direct the fuel axially through outlet 46 in essentially a straight line through the center of the relatively large diameter emulsion tube or passage 26 directly toward outlet 34 so that very little if any of the fuel wets the walls of the emulsion passage; i.e., the fuel flows in a relatively small diameter stream through the center of emulsion passage 26 essentially without contacting the walls of the passage. This minimizes fuel evaporation in passage 26.

Nozzle 44 also is positioned to project into the intersection between air inlet passage 30 and emulsion passage 26 so as to be washedby the flow of air past the nozzle to permit liquid fuel to be drawn from the passage. 50, where the fuel. essential atmosphere pressure acting on it.

As the fuel and air move through emulsion passage 26,

therefore, it will be clear that flow through the relatively large diameter emulsion passage will provide low flow velocities; but, that when the flow reaches outlet 34, the rapidly increased velocities will cause an atomization of the fueldroplets so that they are drawn into induction passage 12in a finely atomized spray. Thus, with the construction described, random fluctuations of fuel flow are essentially eliminated, and a far greater degree of control of the fuel flow is provided than with known idle systems.

FIG. 1 also shows a conventional transfer port 54 that, in this case, straddles the idle speed. position of throttle valve 20. Air flowing into and out of the large transfer slot may form eddies or turbulences which would disturb the fuel flow in passage 26 by creating fluctuation in flow rate. Therefore, in

this case, the transfer slot or. is not connected directly to emulsion passage 26 but by a smallside passage 56 containing an orifice or flow restricting 8 The latter not only perrnits the use of a small passage 56. that reduces the likelihood of liquid fuel-accumulation in the side cavity, but also p ermits the use of a practical size transfer slot or port 54-while isolating the flow fluctuations therein from passage 26.

As thus far described, therefore, it willbe seen that with the throttle valve in its idle speed position shown, air at essentially atmospheric pressure is taken in through. the inlet passage past the orifice 32 due to the normally high vacuum signal in outlet 36 at this time. By virtue the transfer 54 straddling the throttle valve, at this time, the signal inpassage 26 is somewhat less maximum. The vacuum signal in passage 26, however, is sufficient to draw fuel from passage through the. nozzle6 a manner so that it is discharged axially through thec'entjergof. the. passage 26 essentially without contacting the. thereof; It then flows into the outlet 34 with high velocitysothat the fuel dischargedinto the induction passage 'will be, intheform of a finely atomized pmy- "FIGS. 2 and 2a show a mgdifiedrvers ion of the FIG. 1 em; bodiment. More specifically, thefair, inlet passage 3t); corresponding to passage 30 il'tElQ L in this case contains an adjustable variable area orifice, 32f. latter consists of a manually adjustable needle valve projecting into a cooperating portion of passage 31) as shown. Also, the transfer port or slot 54' in thisin eehas a separate connection to the air inlet passage 31] insteadof to the emulsion passage 26 in no. 1. The fixcdarea orifice. 5;; gr no; 1, in

this case, is replaced by an'adjustable variable area orifice 58? provided bya manually adjustable needle valve 62 projecting,

into passage 56. Furthermore, small diameter outlet: passage 36 in this case is connectedto the maininduction passage without the inclusion of the, adjustable screw, 38

shewnin FIG. 1.

'lnall otherrespects, however, HQ. 2 operates essentially the sameas the FlG. lembodiment, The two adjustmen tsto the needle valves 60 and'62 inFlG. 2-are meant tobe a onetime factory fix, andarenot intendedjtobe changed in the field. These adjustments permitcompensating for manufacturilngvariances and for differencesinclimatic areas of use of the carburetor, V i

' BIG. 3- shows a still ful' mqmodification to the carbaretor idle system illustrated inFlGS; 1, 1 6,2 and in FIG 3, emulsion passage 26," at its le wierfend intersects the transfer cavity 56", the latter beingjsolatedfromthe transfer port orslotby abaffle or flowrest'rictor 5 8?. Theupper portion of emulsion passage 26" is connected by an air inlet passage 30" centaining a manually adjust able. needle valve 32" similar to theElG. 2showing.

'The main differencein the F10. 3 embodimentis the inclu= sion or an essentially straight wirelikefuel guide element64, thatextends centrally oraxially throughthe emulsion passage therein as shown. The ends of the wire are wedged in to prevent vibration of the wire.

In operation, the discharge of fuel through nozzle 44" causes the fuel to cling to and flow along the wire surface from the inlet to the outlet portion. The wire core increases the stability of the. fuel jet because the surface tension makes the fuel adhere to the wire. Accordingly, very little if any fuel wets the walls of the emulsion passage 26", which essentially eliminates idle fuel flow fluctuations in the emulsion passage.

Whenthe fuel reaches the high velocityoutlet passage 331", at the end of guide wire 64, the high drag forces between the.

1 air and the fuel break the fuel away from the wire surface and I area.

In each of the instances and embodiments described, it will be clear that the length and size of the emulsion passage and outlet hole will be chosen and controlled to provide the most efiicient and desired operation without obtaining random fluctuations of the fuel flow rate.

' 5 While the invention has'been illustrated and. described in its preferred embodiments, it will be clear to those skilled in the arts to which it pertains that many changes and modifications maybe made thereto without departing from the scope of the invention. For example, the high outlet velocity passage 36' could be made with two different diameters instead of a single constant diameter shown; also, both the low velocity and high velocity emulsion passages could be made shorter, than shown and with irregular shapes so long as the fuel stream is injecteddirectlyinto the hole of the, high velocity emulsion passage. Additionally, the adjustability of the idle mixture can be provided; by an additional adjustable air bypass passage connecting theiair passage of the idle .system.

I claim;

L'An idle air fuel-system for a carburetor having a main induction passage having one end connected to a source of air at essentiallyatmospheric pressure and its other end adapted to be connectedtothe intake manifold of an internal combustion engine to'be subject to the change in vacuum thereinand a throttle valye mounted across said passage to control flow therethroughandrotatably movable between an engine idle speed position essentially closing said main. passage and a second 'position permitting an essentially unrestricted flow therethrough, said-idle system including an air fuel emulsion passagein a circuit.in parallel to said main passage, said emulsionpassagerhaving an air inlet atone end connected to said mainfinductionpassage at a location anterior of said throttle valveanda restricted fuel-air outlet at the opposite end connected to saidginduction passage at a location posterior of said throttlevalve, said one end of saidemulsion passage containing a fueljet connectedto a source of fuel and positioned in the path ofiflow of air therepast from said air inlet and man attitude effectingadischarge of fuel therefrom essentially along the axis ofsaid'emulsion passage, said latter passage being of a' of srnaller cross-sectional area connecting said transfer port to said emulsion passage, and flow restricting means in said latter means to control flow therethrough to minimize disturbances to flowsthroughsaid emulsion passage.

2;. An idlesystem as in claim. 1, saidflow restrictingmeans speed position essentially closingsaid main passage and a second position permitting an essentially unrestricted flow therethrough, said idle system including an air fuel emulsion passage in a circuit in parallel to said main'passage, said emulsion passage having an air inlet at one end connected to said main induction passage at a location anterior of said throttle valve and a restricted fuel-air outlet at the opposite end connected to said induction passage at a location posterior of said throttle valve, said one end of said emulsion passage containing a fuel jet connected to a source of fuel and positioned in the path of flow of air therepast from said air inlet and at an attitude effecting a discharge of fuel therefrom essentially along the axis of said emulsion passage, said latter passage being of a diameter sufficiently large relative to the size of said outlet that wetting of the walls of said emulsion passage by the fuel is essentially eliminated whereby fluctuations in fuel flow rate are minimized, said emulsion passage containing wirelike means extending axially from said fuel jet through said emulsion passage whereby fuel discharged from said nozzle flows along the surface of said latter means and is retained thereagainst by the surface tension thereof, said guide means being mounted at one end essentially in the center of said fuel jet and being supported at its opposite end in said emulsion passage outlet wherein the increased air velocity of the flow therein effects a movement of said fuel away from said wirelike means and through said passage outlet in the form of an atomized spray. 

1. An idle air fuel system for a carburetor having a main induction passage having one end connected to a source of air at essentially atmospheric pressure and its other end adapted to be connected to the intake manifold of an internal combustion engine to be subject to the change in vacuum therein and a throttle valve mounted across said passage to control flow therethrough and rotatably movable between an engine idle speed position essentially closing said main passage and a second position permitting an essentially unrestricted flow therethrough, said idle system including an air fuel emulsion passage in a circuit in parallel to said main passage, said emulsion passage having an air inlet at one end connected to said main induction passage at a location anterior of said throttle valve and a restricted fuelair outlet at the opposite end connected to said induction passage at a location posterior of said throttle valve, said one end of said emulsion passage containing a fuel jet connected to a source of fuel and positioned in the path of flow of air therepast from said air inlet and at an attitude effecting a discharge of fuel therefrom essentially along the axis of said emulsion passage, said latter passage being of a diameter sufficiently large relative to the size of said outlet that wetting of the walls of said emulsion passage by the fuel is essentially eliminated whereby fluctuations in fuel flow rate are minimized, said idle system including transfer port means opening into said main induction passage and straddled by said throttle valve in its engine idle speed position so as to variably control air fuel flow during idle and off idle speeds as a function of the position of said throttle valve, conduit means of smaller cross-sectional area connecting said transfer port to said emulsion passage, and flow restricting means in said latter means to control flow therethrough to minimize disturbances to flows through said emulsion passage.
 2. An idle system as in claim 1, said flow restricting means being adjustable in area.
 3. An idle air fuel system for a carburetor having a main induction passage having one end connected to a source of air at essentially atmospheric pressure and its other end adapted to be connected to the intake manifold of an internal combustion engine to be subject to the change in vacuum therein and a throttle valve mounted across said passage to control flow therethrough and rotatably movable between an engine idle speed position essentially closing said main passage and a second position permitting an essentially unrestricted flow therethrough, said idle system including an air fuel emulsion passage in a circuit in parallel to said main passage, said emulsion passage having an air inlet at one end connected to said main induction passage at a location anterior of said throttle valve and a restricted fuel-air outlet at the opposite end connected to said induction passage at a location posterior of said throttle valve, said one end of said emulsion passage containing a fuel jet connected to a source of fuel and positioned in the path of flow of air therepast from said air inlet and at an attitude effecting a discharge of fuel therefrom essentially along the axis of said emulsion passage, said latter passage being of a diameter sufficiently large relative to the size of said outlet that wetting of the walls of said emulsion passage by the fuel is essentially eliminated whereby fluctuations in fuel flow rate are minimized, said emulsion passage containIng wirelike means extending axially from said fuel jet through said emulsion passage whereby fuel discharged from said nozzle flows along the surface of said latter means and is retained thereagainst by the surface tension thereof, said guide means being mounted at one end essentially in the center of said fuel jet and being supported at its opposite end in said emulsion passage outlet wherein the increased air velocity of the flow therein effects a movement of said fuel away from said wirelike means and through said passage outlet in the form of an atomized spray. 